1. Field of the Invention
This invention relates to a method of measuring fluctuations in the indicated mean effective pressure of an engine and apparatus therefor, and particularly to such a method which is suitable for measuring the combustion stability (cycle work stability) of each cylinder in a multi-cylinder engine for a motor car.
2. Description of the Prior Art
In recent years, necessity has been voiced for improving the fuel consumption rate in engines in motor cars because of the foreseeable exhaustion of energy resources. For this reason, measures have been developed for improving combustion, decreasing friction and so forth, and some of these measures have been put to practical use. For example, setting the idling rotational speed of an engine at a low level has been tried. However, lowering the idling speed tends to increase engine vibrations, causing uncomfortable vibrations and generating increased noise in the transmission and the like. Consequently, it follows that for reduced idling speeds will be problem free, the stability of the engine must be improved, i.e., the fluctuations in the cycle work must be reduced.
Nevertheless, heretofore, in order to measure the fluctuations of the indicated mean effective pressure Pi of a multi-cylinder engine, representing the combustion stability per cylinder of the engine, i.e., the stability of the power generated for each cycle, not only have pressure indicators been mounted on the respective cylinders (because the indicated mean effective pressure Pi has been obtained from an indicator diagram) but also a high-speed data processor has been employed which has a large memory capacity for statistically processing multi-cycle indicator diagrams. For this reason, the manufacturing cost for the measuring apparatus has been very high, handling the measuring apparatus has been troublesome, and it has been difficult to make measurements of fluctuations in the indicated mean effective pressure in a simple way.
Also, devices for macroscopically evaluating the idling stability, including devices for measuring changes in the mean rotational speed, engine vibration width and vibration acceleration, for example, have been used. However, all of these data are dependent upon many factors in addition to variations in rotational speed due to variations in combustion. Furthermore, only superficial data, which have undergone interference of an engine mount, etc., can be obtained, thus presenting disadvantages that the measured values have low physical significance, and moreover, measurements for the respective cylinders cannot be effected.